1. Field of the Invention
This invention relates to a weapon with a relatively high rate of fire and more particularly to an improved weapon having a dual feed mechanism which permits an instantaneous next round selection when switching from one feed mechanism to the other.
2. Description of the Prior Art
Relatively high rate of fire weapons are known which have a single feed mechanism, for example the gun described in U.S. application Ser. No. 789,502, filed Apr. 21, 1977, which is a continuation of U.S. application Ser. No. 418,356, filed Nov. 23, 1973, and now abandoned, and assigned to the same assignee of the present invention.
Improved versions of the gun of Ser. No. 789,502 are disclosed in U.S. application Ser. Nos. 046,664 and 046,665, both filed on June 8, 1979, and assigned to the same assignee of the present invention.
Among the improvements is the provision of a dual feed mechanism, as disclosed in U.S. applications Ser. Nos. 046,664 and 046,665 permitting feeding of the same type of ammunition through one or the other of the feed mechanisms, or permitting feeding of different types of ammunition, one type through each feed mechanism. Where the same type of ammunition is used in each feed mechanism, switching from one feed mechanism to the other creates no noticeable difference in the impact point of the round since the ballistics and the trajectory of the rounds are the same.
Where, however, one feed mechanism feeds one type of round and the other feed mechanism feeds another type of round, there is a one-round delay which may create operational problems if the gunner is not aware of or does not remember to compensate for the differences in ballistics and/or trajectory of the different types of ammunition. In the gun described in U.S. applications Ser. No. 046,664 and 046,665, if a gunner is firing one type of round, for example 25 mm high explosive incendiary (HEI), and switches to another type of round, for example 25 mm armor piercing discarding sabot (APDS), one round of the previously selected ammunition will cycle and fire before the first round of the newly selected ammunition is fed and fired. Normally, either a fire control or sighting mechanism is used which automatically or manually compensates for the difference in trajectory of the various types of ammunition. Thus, with a target at 1000 meters, and assuming a change from HEI to APDS ammunition, one round of HEI remains to be fired. If before the remaining round of HEI is fired, the gunner compensates for the change in ammunition, the result is that gun elevation is reduced (i.e., compensating super-elevation is reduced), and the remaining HEI round will fall short of the 1000 meter target. Conversely, if the change is made from APDS to HEI, one round of APDS remains to be fired. If at the time of the change, the gunner adds elevation (i.e., compensating super-elevation is added) the APDS round fired will pass above the target.
Accordingly, the gunner must be trained to remember that sighting changes should be made after firing the one remaining round of the previously selected ammunition type. This, however, is not always easy to do under the stress of combat, particularl y since the firing mode may have been a rapid fire mode. In this event, the gunner must stop firing, select the other type of ammunition, select the single round mode, fire the remaining round, make the appropriate sighting adjustment, and then select the appropriate firing mode as called for by the operational circumstances.
There are, however, operational circumstances in which it is desired to assure that after a change is made, the fired round of the selected ammunition will be on target. A short round may fall in a friendly zone or a long round may give away the surprise advantage.
To understand why one round of the previously fired type remains to be fired after a change in ammunition types, it is necessary to understand the operation of the guns of the three applications previously identified.
Those prior guns are characterized by a feeder assembly which includes constantly driven in-feed sprockets and an intermittently driven feed rotor. With the gun in the normal cease-fire rest condition, the bolt is to the rear holding the spent casing of the previously fired round. The cooperating feed rotor with the three round pockets is stationary, and a round is in that pocket which is next in the rotor feed sequence. There is also a round in each of the in-feed sprockets. The important point to note is that one live and an empty case are in the feed rotor and irreversibly committed to the firing sequence, one behind the breech and one due to be rotated to the breech position next.
At the start of firing, the motor causes the bolt drive assembly to function as well as the in-feed sprockets. As the master link on the bolt assembly traverses from one side of the chain drive track to the other, the feed rotor is intermittently driven, sweeping out the spent casing and presenting the one round, already in the feed rotor, to the bolt face. At this point, the bolt starts forward, the feed rotor is stationary and the in-feed sprockets remain in motion. T1 round is rammed, fired, and the spent casing withdrawn from the breech and brought to the rear, essentially to the "rest position." Just prior to coming to the rest position the next round drops into the feed rotor. At this point the sequence repeats.
From the above brief description, it can be seen that if an ammunition change is made so that the second round is the newly selected ammunition type, there will be one shot fired of the previous ammunition type, with the possible consequences already discussed.
While it is possible to redesign the gun structure in-feed mechanism completely, or to redesign the gun, there are significant practical advantages in being able to provide a next round selection feed system which will assure that the first round will be the selected type, and to achieve this feature without substantial reconstruction of the gun components.
It is also an advantage to be able to simplify the loading and down-loading of the gun, as compared to earlier versions of the same type of gun.
It is known in the prior art to feed a round into a feed sprocket which is driven at a constant rotational velocity, and to use cam operated buckets which are moved radially, through a cam action, to increase the linear velocity of the round as it is handed-off to the gun bolt. In such a system, which is relatively complex, acceleration of the round is achieved by combination of a constant rotational velocity, of a shaft with radial displacement of the feed buckets, which travel at the same angular velocity as the shaft upon which they are mounted. To use such a system in the dual feed guns described would require substantial redesign of the entire in-feed mechanism.
It would also be an advantage to include in the gun design a feature for avoiding cook-off of a round or thermal ignition.